By means of such catheters liquids can be injected into body cavities, e.g. blood vessels or samples can be taken from body cavities. Such catheters are also used during operations, particularly in operations where the patient is in a semi-sitting position, for the prevention and treatment of air embolisms. Air embolisms can occur when venous vessels are opened and a negative venous pressure prevails as a result of heavy blood loss, e.g. during transplants. Thereby air can be sucked into the central venous system and an accumulation of larger air volumes can occur, blocking the blood flow to the heart.
For the aspiration of such air from the central venous system, the catheter which has at least one opening, is placed in the upper vena cava at the entrance to the right atrium. When a catheter with several lateral openings is used, the point of the catheter is placed rather in the upper half of the right atrium. Through the opening or openings of the catheter, the air which may have entered the central venous system during an operation is aspirated, thereby preventing an air embolism. The disadvantage is that in order to prevent air embolisms such catheters have to be precisely placed, but their placement is not simple because the position of the catheter cannot be exactly determined from the outside.
Besides in addition to the catheter a further instrument is required, in order to detect the air which may possibly have entered the central venous system and to aspirate it by means of the catheter.
Provided that transesophagial echocardiography is used, a flexible tube with an ultrasound device at its end can be introduced into the patient's esophagus. The disadvantage of this method is that the required equipment is very expensive and that the patient has to be monitored by an additional physician not only during the operation, but also for several hours afterwards. So far this method has proven to be very costly.
In another procedure for detecting air embolisms a Doppler probe is affixed from the outside on the body of the patient in the cardiac area. The measuring results obtained this way are partially quite inaccurate since the distance between the Doppler probe affixed to the skin and the heart is large, and the resulting measuring results can be influenced by the hemostatic devices used in the operative tract, such as electrocautery. Furthermore the Doppler probe has to be very precisely placed. With patients with lung enlargement, for instance as the result of bronchitis or asthma, this procedure cannot be used at all.